Question

What are 4 signs that chemical reaction had occurred?

Answer 1

Answer:

Color Change.

Production of an odor.

Change of Temperature.

Evolution of a gas (bubbles)

Precipitate (formation of a solid)  

There are 5 so you can choose 4.

Answer 2

1.Color Change.

2.Production of an odor.

3.Change of Temperature.

4.Evolution of a gas (formation of bubbles)

5.Precipitate (formation of a solid)